This is a blog advocating the overturning and/or ignoring of the controversial IAU planet definition that demoted Pluto, the adoption of a broader planet definition that includes all dwarf planets, and the chronicling of worldwide efforts toward these goals.
We
have once again reached that noteworthy milestone—in the Northern Hemisphere,
it is the Winter Solstice, the shortest day and longest night, the turning
point of the year when darkness stops advancing, and the Sun appears to stand
still in the sky before reversing course.
It’s
been quite a year for space exploration. The James Webb Space Telescope
successfully launched just about a year ago in spite of endless delays and
repeatedly going over budget. It performed flawlessly in unfurling its
sunshield and mirror, reaching its Lagrange Point position, and returning
stunning images that open a new era of exploration for astrophysics, planetary
science, and cosmology.
Another
long delayed project, our return to the Moon, also finally launched this year.
Artemis I sent back beautiful close up photos of both Earth and Moon,
reminiscent of the famous Apollo 8 image captured at this time of year back in
1968—a picture that had a profound impact on many and played a key role in
launching the environmental movement.
While
2022 has certainly had its share of challenges, it brought to fruition projects
some doubted would ever launch, revealing that late does not mean never and
reminding us that if something really matters, giving up should never be an
option.
People
who have had the good fortune to travel to space note it brings a life-changing
perspective. From there, no borders are visible, just one fragile planet, now
home to 8 billion people and numerous other life forms.
We
all, not just world leaders, need that change in perspective because the
problems our home planet faces cannot be addressed by just one group of people
or one country. The only way we have any hope to stabilize our climate,
mitigate the worst effects of climate change, and clean up our air, land, and
water, is to come together as one people on one planet.
Too
often, people look at the year-end holidays in ways that divide us, at a time
when, more than ever, we need to unite to preserve our planet’s habitability
for future generations—so we can one day explore the solar system and
eventually the stars.
This day, at its core, is about hope. It is about light and life, known by the
Romans as the Birthday of the Unconquerable Sun. This makes it an ideal time to
treasure the gift of our planet and affirm the amazing things we can accomplish
when we come together for a common goal—like launching JWST and sending
astronauts to the Moon.
If
we can do those things, we can save our planet for future generations. May the
year that starts with the return of the light inspire us all to come together
and choose a future of light and life.
Space.com is usually a very
credible information site about all matters space and astronomy, which is why
its October 23, 2022 article, “Why
is Pluto Not a Planet?” is so disappointing in its blatant one-sidedness.
More
than 16 years after the controversial IAU vote on a highly flawed planet
definition, it is difficult to understand why this site would publish an
article that is extremely selective in every one of the sources it uses as
references. From the IAU web page to Mike Brown to Ethan Siegel, formerly of Forbes, to a Neil Tyson video, the
article refers almost solely to supporters of the IAU definition and completely
excludes the many essays and articles written from the opposing point of view.
The
article is problematic starting with its title, which, instead of acknowledging
the ongoing debate over planet definition and Pluto’s status, simply states the
IAU view as fact. This misleading title essentially presents the IAU view as “the
truth” rather than as one view in an ongoing debate, and this notion is
repeatedly assumed in the article, in spite of very sparse references to
dissenting views.
Yet,
there is absolutely NO reason to give the IAU position privilege as somehow being
the “official” one in use. It is simply one of several definitions currently
used by planetary scientists.
We need
to address the factual errors in this article. Like many writings on this
subject over the last 16 years, the writers cite Ceres’s discovery as a planet
and subsequent demotion to asteroid in the mid-19th century as an
earlier example of what happened to Pluto. However, they fail to acknowledge
the other, crucial part of Ceres’s history.
Because
it is very small, Ceres could not be resolved into a disk by 19th century
telescopes. At the time, it therefore made sense to demote it to one of many
asteroids in the belt between Mars and Jupiter. However, since then, Ceres has
been found to be spherical, meaning unlike nearly every asteroid in that belt,
it is squeezed into a round or nearly round shape by its own gravity. Most
asteroids are simply rubble piles shaped by chemical bonds. The threshold for
an object being spherical, in a state known as hydrostatic equilibrium, is crucial
because this is when objects begin to experience geology and the complex
processes seen on rocky planets.
In 2015, NASA’s Dawn mission revealed
Ceres to have these complex features, including cryo-volcanoes and a possible
subsurface ocean that could potentially host microbial life. These findings
indicate the 19th century demotion was in error and that Ceres is
more like the larger rocky planets than almost all objects in the asteroid
belt, with the exception of Vesta and Pallas, which appear to have once been
spherical only to have had a large portion knocked off during impacts with
other objects.
Many
scientists argue this makes Vesta and Pallas deserve an intermediate category
between asteroid and small or dwarf planet, such as protoplanet. In fact, some
scientists on the Dawn mission refer
to Vesta as the solar system’s “smallest terrestrial planet.”
While
some, including the writers of this article, invoke Pluto’s eccentric orbit and
17-degree tilt to the ecliptic as reasons for demoting it from planethood, the
fact is several exoplanet systems contain multiple giant planets all orbiting
in different planes. At least two systems have giant planets that cross one
another’s orbits. And the ecliptic, often wrongly depicted as the path of the
Sun, is actually the plane of the Earth in its solar orbit. Requiring objects
to orbit in the same plane as Earth is a violation of the Copernican principle,
which essentially states that Earth is just another planet, not the center of
anything. And if giant objects that cross the orbits of other giant planets in
their systems are not planets, what then are they?
The
next inaccuracy in the Space.com
article is its attribution of Eris’s discovery solely to Mike Brown. While
Brown often presents himself as Eris’s sole discoverer, the fact is, Eris was
discovered by a team of three scientists, the other two being Chad Trujillo and
David Rabinowitz. Significantly, both Trujillo and Rabinowitz reject the IAU
planet definition. Rabinowitz even signed a petition with hundreds of planetary
scientists back in 2006 in response to the IAU definition, saying they would
not use it.
The
reference to the late Brian Marsden is also problematic, as Marsden, who apparently
had a long feud with the late Pluto discoverer Clyde Tombaugh, was obsessed for
decades with demoting Pluto so it could be put under his auspices at the IAU
Minor Planet Center. Like Brown, he is a scientist who appears to have had his
own agenda from the start.
While
the article does acknowledge that only 424 IAU members voted on the controversial
planet definition in 2006, it fails to note that this vote was held in
violation of IAU bylaws, which prohibit putting a resolution to the floor of a
General Assembly without first vetting it by the proper IAU committee. It also
fails to mention that these 424 people were largely not planetary scientists
but other types of astronomers, that they represented only four percent of the
IAU’s membership, that no electronic or absentee voting was permitted, that 91
of the 424 voted for dwarf planets to be classed as a subclass of planets, and
that an equal number of professional planetary scientists signed the afore-mentioned
petition rejecting the IAU definition within days of its adoption.
Additionally,
the writers fail to mention that when initially coined by Alan Stern in 1991,
the term “dwarf planet” was intended to designate an additional class of small
planets, not to designate a class of non-planets. In its unauthorized vote, the
IAU essentially misused the term “dwarf planet” based on the fiction that dwarf
planets are fundamentally different compositionally than their larger
counterparts, a position proved false by the findings of the Dawn and New Horizons missions.
Even Neil Tyson is on record saying he has no problem with dwarf planets being
considered a subclass of full planets!
As
the article writers note, New Horizons found Pluto to have active geology;
diverse features including windswept dunes, varied terrains, a layered
atmosphere, cryo-volcanism, interaction between atmosphere and surface, and a
likely subsurface ocean. Some complex features discovered on Pluto exist
elsewhere in the solar system only on Earth and Mars!
To
make matters worse, the article never acknowledges the alternative geophysical
planet definition, which is preferred by most planetary scientists, beyond a
vague mention of a 2017 proposal that “defined a planet as a round object in
space that’s smaller than a star.” This is a major disservice to the proposal,
presented to the Lunar and Planetary
Science Conference that year, which centers planet definition on an object’s
intrinsic properties rather than on its location, which the IAU definition does.
Most
problematic is the article’s inherent assumption that only the IAU has the
ability or power to determine what a planet is. Conveyed throughout this
article, that sentiment can be seen in the statement noting Alan Stern and
David Grinspoon’s 2018 Washington
Post article urging reconsideration of planet definition “have fallen
on deaf ears so far, and it seems unlikely theIAU
will revisit the controversy any time soon.”
If such pleas to the IAU fall on deaf ears, and the organization refuses to
address new data returned by the Dawn
and New Horizons missions, then it is
time to consider other venues for this discussion. The notion of science being
decided by any type of “authority” went out with Galileo’s discovery of Jupiter’s
moons over 400 years ago. A science publication like Space.com should know better than to appeal to any “authority”
regarding scientific matters.
Finally,
the article falls back on attributing opposition to the IAU decision to
emotion, as seen in its Mike Brown quote, “Nostalgia for Pluto is not a very
good argument, but that’s basically all there is. Now, let’s get on with
reality.”
This comment is not only demeaning; it is also blatantly false. Scientists,
amateur astronomers, and members of the public oppose the IAU definition not
because of nostalgia or emotion but because the geophysical definition, which
classifies objects first and foremost by their intrinsic properties, simply
makes more sense based on what we have discovered about these objects. Brown
does not get to unilaterally end the debate and get the last word simply
because he wants to do so.
There are so many scientists and publications that articulately present the
other side of this debate. I urge Space.com
to do a better job in presenting this fascinating controversy to give readers a
comprehensive understanding of both positions, allowing them to decide for
themselves where they stand.
The
authors of this article are right on one thing: This debate will continue for the foreseeable
future.
Sources in response to those presented
in the Space.com article:
Note: I wrote the response to the IAU statement and to Siegel’s Forbes article and embrace my role in
this debate on Twitter with the handle @plutosavior
.
I have covered the New Horizons mission for the website Spaceflight Insider
since 2014 though the opinion expressed here is solely my own and not
necessarily that of the site or its editors.
“Responding
to the IAU: Pluto and the Developing Landscape of the Solar System,” a
point-by-point rebuttal to the IAU statement:
Sixteen
years. As of today, that is how long it has been since the IAU attempted to end the planet definition
debate once and for all but instead created more chaos and confusion on this
topic for the media, educators, and the general population.
The
spread of misinformation their decision caused unfortunately continues to this
day.
In
the last few years, some people have taken to designating August 24, the day of
the IAU vote, as a “holiday” titled “Pluto Demoted Day.” Writer Aryan Sahu, in
a very one-sided article published on the website Merazone,
actually described this day as “fun” and listed ways to “celebrate” it without
even acknowledging the ongoing controversy. Unfortunately, the usually
informative astronomy site TimeandDate.com also lists this day
as a “fun holiday.”
But
it is not in any way a holiday or something to celebrate.
I instead choose to call it Pluto
Resistance Day. It’s the day when all who recognize the flaws of the IAU
definition come together and affirm our commitment to advocate for a better
planet definition in the long term and educate the public about the ongoing
debate in the meantime.
Although
there are good children’s books on the solar system that present both sides of
the controversy, others that ignore the pro-Pluto view continue to be published.
I cringed when I saw one new children’s book titled Eight Little Planets and another called How to Teach Grownups about Pluto that humorously teaches children
to use the five stages of grief to get the adults in their lives to accept that
Pluto is “gone.”
Yet there is no need for any type of grief because Planet Pluto is alive and
well!
But
the misinformation continues. Just today, an article in The
Abbotsford News erroneously describes Pluto as an “icy stone plodding
around the Kuiper Belt,” then states that “Thousands of objects have been
catalogued so far in that outer belt, the Kuiper Belt, and at least 200 of them are bigger than Pluto.”
Far
from an “icy stone,” Pluto is approximately 70 percent rock. And not a single
object larger than Pluto has been discovered in the Kuiper Belt to date. Eris
was initially thought to be larger but was found to be marginally smaller than
Pluto when a team of astronomers observed it occult a star in 2010.
Yesterday,
an article published in Science News
titled "The
Discovery of the Kuiper Belt revamped our view of the solar system"
failed to even acknowledge the ongoing planet debate, quoting Mike Brown, David
Jewitt, and Jane Luu, all of whom argued that Pluto “does not belong with the
planets” without interviewing or mentioning a single planetary scientist who
disagrees with this statement and favors the geophysical definition. The
geophysical definition was not even mentioned once in the article.
It then goes on to say, "Pluto probably wouldn't be a member of the planet
club much longer, the two (Jewitt and Luu) predicted. Indeed, by 2006, it was
out” with no acknowledgement of the fact that most of the four percent of the
IAU who voted on this were not planetary scientists but other types of
astronomers, that an equal number of planetary scientists signed a petition
rejecting the IAU decision, and that most planetary scientists today ignore
that definition in favor of the geophysical one.
As noted before in this blog, the IAU definition requires a planet to orbit the
Sun, not a star. This means that none of the 5,000 plus exoplanets discovered
to date count as planets under their definition. Neither do rogue planets,
which don’t orbit any star and therefore have no orbit to clear. In 2006, the
IAU leadership promised to address the issue of defining exoplanets, but in 16
years, no such effort has been made.
Meanwhile,
seven years have passed since Dawn’s
flyby of Ceres and New Horizons’ flyby of Pluto, and the IAU
has not shown any interest in using the data from these missions to reconsider
the status of Ceres, Pluto, and other dwarf planets that could potentially have
subsurface oceans capable of harboring microbial life.
Just
two weeks ago, the IAU held yet another General Assembly that didn’t consider
any of these issues.
While
the stalemate continues over planet definition and the IAU continues to do
nothing to correct the confusion their definition has caused, there has been
one major positive development in the last year. Over budget and more than a
decade late, the James Webb Space Telescope (JWST) finally and successfully launched
in the last week of 2021.
On
several occasions, JWST was almost
canceled and/or defunded. Some astronomers even argued the project was not
worth the trouble and expense. And even after launch, so many parts had to work
correctly that many scientists felt genuine trepidation, afraid something would
go wrong.
But
nothing did, and today, JWST is
orbiting the Sun one million miles from Earth and taking unprecedented,
breathtaking photos of galaxies, stars, and planets. It just sent back a
gorgeous image of Jupiter, and I know I’m not alone in hoping it one day images
Pluto as well.
Whether with JWST or another
observatory, it is only a matter of time before we discover dwarf exoplanets the
size of Pluto. Will that discovery have any impact on the IAU?
JWST took much longer to launch than
expected and faced numerous obstacles, including hurricanes and earthquakes,
yet it is now giving us a whole new view of the universe. And one of its
lessons is that good things sometimes take much longer than anyone desired or
anticipated. But late does not mean never.
No
matter how long it takes, we will not give up on a better, more inclusive
planet definition that recognizes dwarf planets as a subclass of planets. We
will NEVER go away. One way or another, the travesty of August 24, 2006, will
be undone. In the meantime, we will continue to inform the media, textbook
publishers, educators, and the general public that the debate continues, that
the geophysical definition is the one preferred by most planetary scientists,
and that the IAU definition is just one of many, not in any way more “official”
or legitimate than any others in use.
For those
interested in reading a very fair and balanced account of the history and
current state of the planet definition debate, writer Matt Williams has published
an excellent article on the website Interesting
Engineering, which includes quotes by Alan Stern, Phil Metzger, and
yours truly. I am very grateful to him for giving me a voice in his
comprehensive article and encourage all Pluto fans and those interested in this
issue to give the article a read.
This is a response I sent to the one-sided article "Searching for Planet 9" published April 19, 2022, in Big Think by writer Tom Hartsfield along with a request that I or another writer be given the chance to write a response presenting the other side of this ongoing debate.
As you are likely well aware, the debate over planet definition and over Pluto's status remains ongoing. Just four percent of the IAU voted on the controversial demotion of Pluto and related planet definition, and most were not planetary scientists but other types of astronomers. Their decision was immediately opposed by an equal number of planetary scientists in a formal petition led by New Horizons principal investigator Alan Stern.
Notably, the four percent of the IAU who voted on this misused the term "dwarf planet," which Stern coined back in 1991 to refer to a new subclass of planets by stating in their resolution that dwarf planets are not planets at all but another type of object entirely. Nine years later, this statement was not borne out by the findings of the Dawn mission at Ceres and the New Horizons mission at Pluto.
Since the 2015 New Horizons mission revealed Pluto to be a geologically active world with complex processes seen elsewhere in the solar system only on Earth and Mars, an increasing number of planetary scientists have come to view it as a full-fledged planet
At the Lunar and Planetary Sciences Conference in 2017, planetary scientist Kirby Runyon introduced the geophysical planet definition, which rejects the notion that an object has to clear its orbit to be a planet. Unlike the IAU definition, the geophysical definition focuses on objects' intrinsic properties rather than their location and deems any object that is not a star but is large enough and massive enough to be rounded by its own gravity a planet.
Because so many planetary scientists prefer the geophysical definition, they object to the term "Planet 9" for the hypothetical but as yet undiscovered planet in the outer solar system. Advocates of the geophysical definition count dwarf planets as full planets, so they view the solar system as already having a minimum of 13 planets and counting. In the August 5, 2018, edition of Planetary Exploration Newsletter, a publication of the Planetary Science Institute, a group of planetary scientists objected to the insensitive, one-sided use of the term "Planet 9," noting the IAU planet definition is "far from universally accepted."
Instead, they requested this hypothetical world be referred to by the standard term for a hypothetical but as yet undiscovered planet, which is "Planet X," with "X" referring to the unknown rather than to the number 10.
Hartsfield's article unfortunately begins with an extremely one-sided statement, "The former planet 9, Pluto, was knocked out of the club because it failed to meet the definition of a planet" without noting that that definition is just one of several currently in use and remains controversial to this day.
It then continues with the article's first sentences reading, "Our solar system once possessed nine planets. Then we kicked Pluto out of the club because it was just one of several little things beyond Neptune. Pluto happened to be the largest of them, putting it right on the line between planet and Kuiper Belt speck. The hunt is on for the real planet 9--if it exists."
This sentence contains multiple problems. There is no "we" that kicked Pluto out of the club. The sentence assumes a level of consent that never existed, especially among planetary scientists. It does not even acknowledge the fact that most planetary scientists reject the IAU definition and have done so for over 15 years.
Furthermore, Pluto is far from a "Kuiper Belt speck" or even an object between a planet and a speck. Such a statement totally ignores the New Horizons findings, which found Pluto to have planetary processes such as geology and weather, likely geological layering, floating glaciers, a layered atmosphere, interaction between its surface and atmosphere, varied terrains, windswept dunes, cryovolcanism, and a likely subsurface ocean. No Kuiper Belt "speck" has these features; such specks, like asteroids, are simply loosely held together by their chemical bonds.
Big Think's readers deserve a far more fair and balanced reporting of this issue, which acknowledges the ongoing debate and both positions instead of portraying one side as fact. There are many planetary scientists who would be happy to write about this for you, and I would be happy to get you in touch with them.
I sent the message below to several editors at Salon.com regarding an article by Matthew Rosza, published on April 17, 2022, titled, "Pluto Wasn't the First: A Brief History of the Solar System's Forgotten Planets" because the majority of this article is very one-sided in terms of the planet definition debate and therefore calls for a response.
I am writing to request you publish an article of mine responding to Matthew Rosza's April 16,2022, Explainer article, "Pluto Wasn't the First: A Brief History of the Solar System's Forgotten Planets." Although at its end, this article acknowledges that some scientists reject the controversial IAU demotion of Pluto, it is mostly very one-sided in its depiction of the planet debate and Pluto controversy, and unfortunately, there is no comments section on the site for people to respond.
Rosza neglects several important points, beginning with the fact that just four percent of the IAU voted to demote Pluto, and most were not planetary scientists but other types of astronomers. Their decision was immediately opposed in a formal petition by an equal number of professional planetary scientists, yet the mainstream media never reported this fact.
Kindergartners in 2006 did not necessarily .learn a different number of solar system planets than those in 2005 did because many educators also opposed the controversial demotion of Pluto and continued to include Pluto when teaching the solar system.
The analogy to Ceres, made for the last 15 years, is also flawed. According to the geophysical planet definition, which most planetary scientists prefer, Ceres IS a planet because it is rounded by its own gravity, a state known as hydrostatic equilibrium. However, this was not known in the 19th century when it was demoted, because telescopes of the time could not resolve Ceres into a disk. Now they can, which is why it is clear the 19th century demotion was in error. Vesta and Pallas are also not really asteroids; they are considered protoplanets because they appear to have once been spherical only to have had a portion lobbed off in an impact. This makes them very different from true asteroids, which are tiny, shapeless, and held together only by their own chemical bonds.
Additionally, Pluto may have a frozen surface, but data and images from the 2015 New Horizons flyby strongly suggest it has a subsurface liquid ocean (which Ceres may also have) and an internal heat source. This means both Pluto and Ceres are more akin to icy moons like Europa and Enceladus and could potentially support microbial life. While Pluto is often described as an ice world, it is actually 70 percent rock and likely geologically differentiated into core, mantle, and crust just like Earth is.
Saying astronomers once thought Pluto and Ceres should be planets but then "changed their minds" and that Pluto "lost its planet status" because "astronomers had decided there were three criteria for being considered a planet" is an incorrect over-generalization because these decisions were made by only a small number of professionals and largely by those in fields of astronomy other than planetary science. There was NEVER a consensus among planetary scientists on this. Furthermore, saying Pluto "lost its planet status" because of a vote inherently assumes science is done by decree of "authority," a very unscientific statement that essentially went out with Galileo.
Furthermore, the four percent of the IAU who voted on the 2006 resolution misused the term dwarf planet, which was coined by New Horizons principal investigator Alan Stern in 1991. He coined this term to designate a new subclass of planets, not to designate a class of non-planets. In astronomy, dwarf stars are a subclass of stars, and dwarf galaxies are a subclass of galaxies. Claiming that dwarf planets are not planets at all makes no sense and runs counter to the findings of the Dawn and New Horizons missions, which found both Ceres and Pluto to have planetary processes similar to those of the terrestrial worlds.
As a science writer and blogger who has run a blog opposing the IAU decision for over 15 years and has written and spoken extensively on this topic, I respectfully request you allow me or someone else (ideally a planetary science) to write a response to this article clarifying these points and explaining that this issue has been and remains a subject of ongoing debate.
Ninety-two years ago today, on February 18, 1930, Clyde Tombaugh discovered the planet Pluto while blinking photographic plates of the night sky taken several nights apart at Lowell Observatory in Flagstaff, Arizona. In the decades since then, Pluto’s discovery has become more appreciated and more celebrated than he could have imagined on that day.
Once again, the Lowell Observatory is celebrating the anniversary with a multi-day “I Heart Pluto” festival. This year’s is a hybrid event, with many online presentations as well as an in-person evening of entertainment and activities tonight at the Orpheum Theater and a historic walk tracing the steps Clyde Tombaugh took on that day following his discovery. Tombaugh actually spent that evening at the very same Orpheum Theater.
A source at the observatory informed me that tonight’s presentation will be recorded and placed online in the near future.
While more people than ever are coming to appreciate and celebrate this small, unique planet, something interesting is happening. Supporters of the IAU planet definition and of Pluto’s demotion constantly argue that few people care about Pluto’s planet status, that only a few “holdouts” refuse to accept the demotion.
Yet every time Pluto is in the news, this claim is proven to be blatantly false.
This week, Edward Gleason of the Southworth Planetarium in Portland, Maine, who supports Pluto’s planet status, addressed the debate over Pluto’s planet status in an email message sent to friends of the planetarium. The next day, he followed up with a post stating that he received multiple responses on this issue, “all of which were in equal measure thoughtful and passionate.”
He even quoted my response to his question, "The IAU General Assembly is convening its next meeting this August in Korea. Will Pluto's planetary status be then reinstated?" in which I noted that we don’t need the IAU for Pluto to be considered a planet.
I wrote: “Statements like this assume that only the IAU has the right to bestow planet status on an object. This is essentially an appeal to authority. The IAU planet definition should not in any way be privileged above other definitions currently in use, such as the geophysical definition. I have long suggested planetary scientists form their own organization and adopt their own definition of planet. We do not need the IAU to issue a decree or stamp of approval for Pluto to be considered a planet. Unfortunately, the media has portrayed the IAU decision as fact rather than as what it really is--one side in an ongoing debate.”
And he agreed, stating: “Indeed! That line does presuppose that the IAU stands as the final authority on all such matters. We know that most planetary scientists have ignored the IAU's designation, a fact little mentioned by most media sources. I stand cheerfully corrected.”
Gleason’s experience receiving so much feedback regarding Pluto is not unique. Planetary scientists and amateur astronomers who do public presentations and/or write articles on this subject are regularly asked about Pluto and its planet status. Fascination with this tiny, active world, and healthy skepticism about the IAU decision has only grown stronger over the last 15-and-a-half years.
When someone, whether a scientist, a writer, an amateur astronomer, or a member of the public claims that no one cares about Pluto’s status, what they are really saying is that they think no one should care. It usually means they support the IAU planet definition and its claim that dwarf planets are not planets and want to have the last word on the issue.
And their related statement, that Pluto doesn’t care what we call it, is irrelevant. The issue isn’t whether Pluto cares, but why we should care. As Philip Metzger notes, taxonomy is how we make sense of the world. It is integral to science. The IAU’s taxonomy is flawed because it lumps two very different types of objects—asteroids and comets on the one hand, and dwarf planets on the other—into the same category of non-planets.
Too often, one will read articles online that claim our solar system has just two types of planets—terrestrials and jovians—and/or cite the names of the four terrestrials and the four jovians, then add in the asteroid belt and Kuiper Belt to describe the solar system.
But objects like Ceres and Pluto are far more than just small objects in belts, and they differ significantly from the majority of the tiny objects in those belts. Describing the solar system as having just rocky planets, gaseous planets, the asteroid belt, and the Kuiper Belt erases the existence of these small planets, which have more in common with rocky worlds like Earth and Mars than they do with KBOs like Arrokoth.
In a presentation on the glass plates which were used in Pluto’s discovery, one of Lowell Observatory’s speakers who knew Clyde Tombaugh reported that Tombaugh said he immediately recognized the tiny dot whose position moved against the background stars from one plate to another via the blink comparator. That tiny dot is part of a huge star field, and most people aren’t likely to find it even after hours of blinking the two plates.
Pluto was discovered in a unique way, by a very unique, intelligent, and skilled individual. The people of the world deserve to know about this amazing, very much alive little planet. Typically, the more they learn, the more their fascination grows.
In spite of the IAU’s decade-and-a-half false narrative, the people have spoken. And they continue to overwhelmingly recognize Pluto—and all dwarf planets--as a planet.
Lowell Observatory's annual "I Heart Pluto" Festival, celebrating the 92nd anniversary of Pluto's discovery on February 18, 1930, at the observatory in Flagstaff, Arizona, will this year be a combination of in-person and virtual events that will run from today, February 12 through Monday, February 21. You can find the entire schedule of events listed on the event's website. Speakers include Dr. Alan Stern; Dr. Cathy Olkin; Dr. Richard Binzel, former astronaut Dr. Nancy Currie-Gregg, Alden Tombaugh, son of Pluto discoverer Clyde Tombaugh, and many more. Don't miss this annual celebration of our favorite planet!
Depiction of all spherical worlds in the solar system with diameters under 10,000 kilometers. Credit: NASA / JPL, JHUAPL/SwRI, SSI, The Planetary Society, and UCLA / MPS / DLR / IDA, processed by Gordan Ugarkovic, Ted Stryk, Bjorn Jonsson, Roman Tkachenko, and Emily Lakdawalla
The paper’s authors are Philip Metzger, Will Grundy, Mark Sykes, Alan Stern, Jim Bell, Charlene Detelich, Kirby Runyon, and Michael Summers. These scientists conducted an extensive study of planet definition over 400 years (since the time of Galileo) and found that the geophysical planet definition is the one that has been used most since then and the one most consistent with the Copernican Revolution, in which the Sun, rather than the Earth, was recognized as the center of the solar system.
This paper is not centered on Pluto at all but focuses on spherical moons of planets, noting they were considered planets from the time of Galileo until the 19th century, when astrologers, folklorists, and almanac writers needed to keep the number of planets small and orderly to do horoscopes and make weather predictions.
When Galileo first turned his telescope on the Moon, he saw mountains that resembled those on Earth, from which he realized the Moon is also a planet with features similar to those on the Earth. Then, when he discovered the four largest moons of Jupiter, he described them as “four planets circling the star of Jupiter.” This latter point is noted in David Weintraub’s 2007 book, Is Pluto a Planet?
For most of the last 400 years, planets were defined not by their orbital positions, which can and do change, but by their geophysical and geological processes. Spherical moons were classed as secondary or satellite planets, as they clearly have the same processes that primary planets do.
When the IAU adopted its 2006 definition, a strong motivation was keeping the number of solar system planets small, supposedly so children can memorize them. This need for a small number of planets in a neatly, ordered solar system, in which all orbit on the same plane, was an erroneous concept based on culture rather than science.
“This might seem like a small change, but it undermined the central idea about planets that had been passed down from Galileo. Planets were no longer defined by virtue of being complex, with active geology and the potential for life and civilization. Instead, they were defined by virtue of being simple, following certain idealized paths around the Sun,” noted study lead author Philip Metzger of the University of Central Florida (UCF).
As noted previously on many occasions, memorization of a list of planet names is an archaic method of teaching the solar system that dates back to before the space age, when little else was known about the planets other than their names. Today, memorization makes little sense and teaches nothing about the actual planets.
A better method of education involves teaching planet as a broad umbrella category and then focusing on the major characteristics of each planet subclass. Just like students have access to the entire Periodic Table available to them, they can be given complete lists of the solar system’s many planets for reference without having to memorize anything.
Dr. Becky even admitted in her video that this paper is making her take a second look at the planet definition issue. Several commenters on various websites said the same thing.
In addition to changes of mind by people who formerly supported the IAU definition, there are now new books either out or scheduled to be published that take a pro-geophysical definition stand.
Welcome Back Pluto: We’re Glad that You’re a Planet Again by Ron Toms, published in October 2021, explores the weaknesses of the IAU planet definition and actually ends with a chapter titled, “How You Can Make Pluto a Planet Again.”
Of course, Pluto never stopped being a planet. A vote by 333 people does not have the power to change what Pluto is. This section should be worded, “How You Can Make Pluto Recognized as a Planet Again.” Nevertheless, this is very encouraging, and I urge all interested in this subject to purchase this book. I intend to do so myself and to review it on this blog.
In his book, Toms states what many of us have been repeating for more than 15 years: “Don’t fall victim to the logical fallacy known as appeal to authority. The IAU’s definition of planet does not pass scrutiny in spite of their self-proclaimed authority. Anyone can do this. The emperor has no clothes.”
Toms goes on to take issue with the claim that the IAU definition is somehow the “official” one, pointing out that anyone can create a definition and call it “official.”
Within a Facebook discussion of the planet definition controversy, one writer announced plans to write a children’s book about the Kuiper Belt from the standpoint of the geophysical planet definition. I will present more information about this project as it becomes available.
This is an amazing turn of events, and we have the authors of the Icarus article, who spent five years going over four centuries of planetary science literature, to thank for it.
New York Times science writer Ken Chang embedded a poll in his article asking people questions not just about Pluto but also whether Eris and Earth’s Moon should be considered planets. Unfortunately, too few people are familiar with Eris, and too many Pluto supporters advocate only the nine-planet solar system. But even this does not work in favor of the IAU or its problematic definition. A major reason few people learned about Eris and about the geophysical definition is that the IAU vote was centered completely on Pluto. The media story was their removal of Pluto, not the discovery of additional planets in our solar system. So kids are actually learning less about the solar system now than they did prior to the IAU vote, unless their teachers choose to teach a more inclusive view of the solar system.
The poll is therefore not an indictment of Pluto supporters but of the mainstream media, textbook publishers, and educational systems that blindly adopted the IAU position back in 2006 rather than question it, learn the entire story behind it, and teach the controversy.
Back in the 1600s, church leaders refused to look through Galileo’s telescope, which would have enabled them to learn that his discoveries were real and correct. Today, it seems we’re stuck with another so-called “authority” that refuses to look at the latest data on everything from missions to dwarf planets to history to the discovery of exoplanets, all so they can stick to their dogma. If history has anything to say about this, the latter view will not prevail.
I will be writing more later about the planet definition debate heating up again, thanks to a paper published in the journal Icarus explaining why the IAU planet definition is based on astrology and folklore. For now, New York Times Science writer Ken Chang is holding an active poll in an article he wrote today, not just about Pluto's planet status but on the geophysical planet definition. Too many people have responded in favor of just a nine-planet solar system as opposed to one based on the geophysical defintiion, in which Eris, all dwarf planets, and spherical moons are counted as planets. Please visit the article and answer all the questions in support of the geophysical definition. This is not just about Pluto!
I am a freelance writer and community activist who has worked on many progressive and Democratic political campaigns over the last 25 plus years and a lifelong resident of Highland Park, NJ. I have a BA in Journalism from Rutgers University, an MA in Middle East Studies from Harvard University, and an MEd in English Education from Rutgers Graduate School of Education. An enthusiastic amateur astronomer, I have just completed Swinburne University Astronomy Online's Graduate Certificate of Science in astronomy and am pursuing a Masters of Science in astronomy at Swinburne. I am also an actress with experience in theatre and film and have written a full length play. I am currently working full time on a book "The Little Planet That Would Not Die: Pluto's Story."
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